LTE X2 Handover Messaging - EventHelix.com

1 Design with sequence diagrams telecom systems engineering object oriented designLTE X2 Handover Messaging 2013 Rights design with sequence diagrams telecom systems engineering object oriented designLTE X2 Handover Sequence Diagram 2013 eNodeBMMEUEX2AP Handover Request AcknowledgeSGWX2AP Handover RequestSource eNodeBX2AP SN Transfer StatusS1AP Path Switch RequestModify Bearer RequestModify Bearer ResponseS1AP Path Switch AcknowledgeX2AP UE Context ReleaseTracking Area Update RequestTracking Area Update ResponseHandover CommandHandover ConfirmBegin forwarding downlink data from source to destination eNodeBMarks the end for design with sequence diagrams telecom systems engineering object oriented designSource eNodeB Target eNodeBX2AP Handover RequestX2AP Handover Request (Initiating Message)Old eNB UE X2AP IdCauseHandover desired for radio reasonsTarget Cell IdPLMN IdentityeUTRAN Cell IdentifierGUMMEI IdGU Group IdPLMN IdMME Group IdMME CodeUE Context InformationMME UE S1AP IDUE Security CapabilitiesAS Security InformationKey eNBeRABs to be Setup ListeRAB 0eRAB IdeRAB Level QoSParametersQCIUL GTP Tunnel EndpointTransport Layer AddressGTP N-1 RRC Context eNodeB decides to initiate an X2 Handover based on: UE reported RRC downlink signal quality measurements Uplink signal quality measured at the eNodeB eNodeB picks the target cell id for the Handover .

2 X2 Handover is initiated if the If the target cell is served by the same MME as the current cell The message includes UE context information that identifies the UE on the S1AP interface. Security parameters are also included in the message Information about the radio bearers is included in the message. The per RAB information includes QoSparameters GTP Tunnel Information The message also includes RRC context information 2013 design with sequence diagrams telecom systems engineering object oriented designTarget eNodeB Source eNodeBX2AP Handover Request AcknowledgeX2AP Handover Request Acknowledge (Successful Outcome)Old eNB UE X2AP IdNew eNB UE X2AP IdeRABs Admitted ListeRAB Admitted Item 0eRAB IdUL GTP Tunnel EndpointTransport Layer AddressGTP TEIDDL GTP Tunnel EndpointTransport Layer AddressGTP Admitted Item N-1 Transparent ContainerTarget to Source eNB Payload The target eNodeB receives performs admission control on receipt of the Handover Request.

3 The target eNodeB responds with X2AP Handover Request Acknowledge. Information about the accepted RABs is included in the message. The Uplink and Downlink GTP Tunnel information is included for each RAB. The tunnel assignments are made at the target to transport traffic during the Handover . A Handover Command message sent via a transparent container. The source eNodeB send this message to the UE. 2013 design with sequence diagrams telecom systems engineering object oriented designSource eNodeB Target eNodeBX2AP SN Transfer StatusX2AP SN Status Transfer (Initiating Message)Old eNB UE X2AP IdNew eNB UE X2AP IdeRABs Subject to Status TransfereRAB Subject to Status Transfer 0eRAB IdUL Count ValuePDCP SNHFNDL Count ValuePDCP Subject to Status Transfer N-1 The source eNodeB now sends the SN Transfer Status The following fields are present for each RAB The uplink PDCP sequence number Uplink Hyper Frame Number The downlink PDCP sequence number Downlink Hyper Frame Number These fields are needed for continuing ciphering and integrity protection after the Handover .

4 2013 design with sequence diagrams telecom systems engineering object oriented designTarget eNodeB MMES1AP Path Switch RequestS1AP Path Switch RequesteNB UE S1AP IDeRABs to be Switched DL ListeRABs to be Switched DL Item 0eRAB IdTransport Layer AddressGTP to be Switched DL Item N-1 EUTRAN CGIPLMN IdCell IdTAIPLMN IDTACUE Security CapabilitiesEncryption AlgorithmsIntegrity Protection Algorithms The target eNodeB requests switching of the S1-U GTP tunnel towards the target eNodeB. The MME identifies the UE with the eNB to UE S1AP ID The message includes the new cell id and the tracking area id Security capabilities of the target eNodeB are also included. 2013 design with sequence diagrams telecom systems engineering object oriented designMME SGWM odify Bearer RequestModify Bearer Request (initiating message)Bearer Context to be UpdatedEPS Bearer IdS1-U eNodeB F-TEIDTEID/GRE Key The MME requests the SGW to switch the path to the target eNodeB.

5 The S1-U TEID received from the target eNodeB is passed to the SGW. 2013 design with sequence diagrams telecom systems engineering object oriented designSGW MMEM odify Bearer ResponseModify Bearer Response (initiating message)Bearer Context UpdatedEPS Bearer IdS1 SGW F-TEIDTEID/GRE Key SGW updates the bearer and responds back 2013 design with sequence diagrams telecom systems engineering object oriented designS1AP: MME Target eNodeB S1AP Path Switch AcknowledgeS1AP Path Switch RequestMME UE S1AP IDeNB UE S1AP IDeRABs to be Switched UL ListeRABs to be Switched UL ItemeRAB IdGTP TEIDS ecurity Context The target eNodeB requests switching of the S1-U GTP tunnel towards the target eNodeB. The MME identifies the UE with the eNB to UE S1AP ID The message includes the new cell id and the tracking area id Security capabilities of the target eNodeB are also included. 2013 design with sequence diagrams telecom systems engineering object oriented designTarget eNodeB Source eNodeBX2AP UE Context ReleaseX2AP UE Context Release (Initiating Message)Old eNB UE X2AP IDNew eNB UE X2AP ID Sent when the target eNodeB has successfully completed the path switching and radio signaling for the Handover .

6 2013 design with sequence diagrams telecom systems engineering object oriented designUE-NAS MME-NAST racking Area Update RequestTracking Area Update RequestUplink NAS TransporteUTRAN-CGIPLMN IdCell IdTAIPLMN IdTACT racking Area Update RequestEPS Update TimeTA UpdatingOld GUTIM-TMSILast Visited Tracking AreaEPS Bearer Context StatusBearer Context Active Sent if the just completed Handover resulted in a Tracking Area Update 2013 design with sequence diagrams telecom systems engineering object oriented designMME-NAS UE-NAST racking Area Update AcceptTracking Area Update RequestTracking Area Update ResultEPS Update ResultTA UpdatedT3412T3402 Sent if the just completed Handover resulted in a Tracking Area Update 2013 design with sequence diagrams telecom systems engineering object oriented designThank YouLinksDescriptionLTE X2 Handover Sequence DiagramsDetailedmessage flow analysis of LTE X2 handoversEventStudio System DesignerSequence diagram based systemsengineering ProtocolAnalyzerWireshark based visual protocol analysis and system design reverse engineering Call FlowsGSM, SIP, , ISUP, LTE and IMS call DiagramsTCP/IP explained with sequence Networking SoftwareReal-time and embedded systems, call flows andobject oriented design articles.

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